Aries

byTammy PlotneronOctober 13, 2008

Aries

Aries is a faint constellation of the zodiac, positioned on the ecliptic plane between between Pisces to the west and Taurus to the east. Only its Alpha and Beta stars – Hamal and Sheratan – are easy to recognize. They represent the head of the Ram. Teegarden’s star, a recent discovery in the constellation of Aries, is one of Sun’s closest neighbors around 12 light years away. It appears to be a red dwarf, a class of low temperature and low luminosity stars. This would explain why it was not discovered earlier, since it has an apparent magnitude of only 15.4!

In mythology, Aries is the Ram – perhaps the golden one who saved Helle and Phrixos from a king Cretheus for false accusations. Aries the Ram is the also the first astrological sign in the Zodiac – associated with masculinity. Under the tropical zodiac, the Sun is in Aries roughly from March 21 to April 19, by definition beginning at vernal equinox. The vernal equinox has moved in the constellation Pisces, but sometimes it is still called the first point of Aries. It is bordered by constellations of Perseus, Triangulum, Pisces, Cetus and Taurus.

For the unaided eye and observing with binoculars, check out Alpha Arietis – Hamal – its name literally translates to “head of the sheep”. It has the most accurately-measured angular diameter – 0.00680″ (the width of a cent coin seen from 60 km away) – of all but one star and is
some 55 times brighter and five times more massive than our Sun. Not bad for a star that’s still 66 light years away from our solar system! Now have a look at Beta Arietis – Sheratan. Beta shines at magnitude 2.7 and it is located 60 light years from Earth. Back at the turn of the 20th century it was discovered to be a spectroscopic binary, with a period of 106 days. According to Jim Kaler’s fine research; “Sheratan stands out as a result of the extremely high eccentricity of the orbit (0.88), the companion trapped in a record-holding elongated path. Moreover, the star is an observational treasure. The two stars are so close together that they cannot be separated directly through the telescope; all we ever actually see is one star (again common, as to allow detection via the spectrum requires the stars to be close and moving quickly). However, sophisticated observation of Sheratan with an interferometer, a device that makes use of the interfering properties of light to resolve ultra-fine detail, allow (as for the brighter component of Mizar) the pair to be resolved. The masses of the stars (through gravitational theory) can then be measured with high accuracy. Averaging 0.64 Astronomical Units apart (89 percent Venus’ distance from the Sun), a star with the mass of the Sun (1.02 solar) orbits a double-solar-mass (2.00) star every 107 days. Since luminosity is very sensitive to mass, 95 percent of the light of the system is produced by the heavier star. The huge eccentricity adds the spice. As they wheel around each other, the smaller one (undoubtedly a class G star like the Sun) approaches as close as 0.08 AU (only 20 percent Mercury’s distance from the Sun), and then half an orbit later loops around at 1.2 AU, 16 times farther away and 20 percent farther than Earth from the Sun. No close planets could survive the gravitational onslaught. Such stars, in which the doubling is “visible” by two techniques (only about 40 are known, Sheratan one of the brighter), allows accurate assessment of the theoretical relation between stellar mass and luminosity, and provides powerful evidence that the theory is correct. The higher mass star will die first. In a couple billion years, the lower mass G star will be the king of the pair, while the current luminary will be a shrunken dim white dwarf.”

Now let’s move on to some observing with a small telescope! A personal favorite of mine is Gamma Arietis – Mesarthim. This is an easy, wide, double star with blue/white members of matched 4.6 magnitude. One a note of curiosity, Mesarthim was one of the very first double stars to be discovered by Robert Hooke while looking for a comet in 1664! Another easy one binary star is Lambda, it is also a very wide double with a 5th magnitude primary and 5th magnitude secondary. For something a little harder, try 5th magnitude Pi. This one is tight! The 8.8 magnitude companion is on 3 arc seconds away and will really test the resolving power of your optics and the stability of your skies. Use your highest power. If you don’t have luck, try 30 Arietis. The magnitude 7 primary star is a lovely golden yellow and the secondary is about magnitude 8 and is a distinct blue separated by about 40 arc seconds.

For a nice outreach project, try observing 53 Arietis – the “Runaway star”. Along with AE Aurigae and Mu Columbae 53 Arietis appears to be crusing right along from the region of the Great Orion Nebula!

Although Aries isn’t exactly noted for having a great deep sky observing reputation, there are a few objects worth hunting down. For small telescopes, spiral galaxy NGC 772 can be picked up and shows some spiral galaxy structure to larger instruments. NGC 697 is definitely a large telescope only spiral galaxy at 13th magnitude and party of a galaxy group. NGC 972 is also part of a galaxy group and is equally faint at magnitude 12. For die hard fans, try 12th magnitude NGC 1156. It is a dwarf irregular galaxy considered a Magellanic-type with a larger than average core and a a H II nucleus containing zones of contra-rotating gas. The counter-rotation is thought to be the result of tidal interactions with another gas rich galaxy some time in the past. The AGES survey has discovered a candidate dark galaxy close to NGC 1156, one of only a few so far found.

Aries is home to several meteor showers. The May Arietids are a daylight meteor shower which begins between May 4th and June 6th with maximum activity happening on May 16th. Try using an external FM antenna and listening to a low band frequency that doesn’t pick up a clear signal for meteor scatter. The Epsilon Arietids are also a daylight occurrence.. The are active between April 25th to May 27th with peak activity on May 9th. The very best Daytime Arietids occur from May 22nd to July 2nd with a maximum on June 8th, when the meteoroid stream produces one meteor every minute.

Historically speaking, the Delta Arietid meteor shower was first noted in 1959 by analyzing photographic meteor orbits. Don’t be disappointed by just radio activity, because this one can be observed visually and activity occurs between December 8th and December 13th. The Autumn Arietid meteor shower begins on or about September 7th and runs through October 27th. Maximum activity occurs about October 8th, and the fall rate is about 3 to 5 (average) meteors per hour.

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.